1. Field of the Invention
The present invention relates to a circuit configuration having a transceiver circuit and a bus system node having such a circuit configuration.
2. Description of Related Art
Control units, sensor systems and actuator systems in a motor vehicle or commercial vehicle in particular are often interconnected with the help of a communication system such as the bus system known by the FlexRay brand name. Communications traffic on the bus system, access mechanisms and receiving mechanisms, as well as error handling are regulated via a protocol. FlexRay is a fast, deterministic and error-tolerant bus system for use in motor vehicles in particular. The FlexRay protocol operates according to the principle of time division multiple access (TDMA), in which fixed time slots are assigned to subscribers and to the messages to be transmitted; during these time slots, the subscribers have exclusive access to the communications link. The time slots are repeated in a fixed cycle, so that the point in time when a message is transmitted over the bus is precisely predictable, and bus access is deterministic.
To optimally utilize the bandwidth for transmission of messages on the bus system, FlexRay subdivides the cycle into a static part and a dynamic part. The fixed time slots are in the static part at the beginning of a bus cycle. The time slots are dynamically predetermined in the dynamic part. Exclusive bus access is then enabled only for a short period of time, for the duration of at least one so-called minislot. The time slot is lengthened by the required time only if bus access occurs within a minislot. Bandwidth is thus used only if it is actually needed. FlexRay communicates via two physically separate lines, each at a data rate of max. 10 Mbit/sec. FlexRay may also be operated at lower data rates. Channels implemented via these lines correspond to the physical layer, in particular the so-called OSI (open system architecture) layer model. Two channels are used mainly for redundant and thus error-tolerant transmission of messages, but different messages may also be transmitted, which would then double the data rate. The messages are usually transmitted with the help of a differential signal, i.e., the signal transmitted over connecting lines is obtained from the difference between the individual signals transmitted over the two lines. The layer above the physical layer in the layer model is designed in such a way that an electrical or an optical transmission of the signal(s) over the line(s) or transmission by another route is possible.
When such a bus system is used in a vehicle in particular, care must be taken to ensure that the nodes of the bus system consume little power when not actually needed. This may be the case, for example, when functions to be executed by the nodes are not active or when the vehicle is not in operation. The nodes therefore have an idle mode in which a few parts of the nodes are deactivated. When changing from the idle mode to an operating mode, the microcontroller must be completely restarted, which takes a relatively long time. This results in a substantial delay in leaving the idle mode. The nodes of the bus system in the idle mode are thus able to respond to a certain event only with a relatively long response time.